Amplifier protective circuit



Feb. 13, 1951 H. M. WILSON AMPLIFIER PROTECTIVE CIRCUIT Filed July 22, 1949 Patented Feb. 13, 1951 UNITED STATES PATENT OFFICE Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., a corporation of Delaware Application July 22, 1949, Serial No. 106,227

9 Claims.

This invention relates generally to a protective circuit for an electronic control device and. is more particularly concerned with preventing operation of the device when there is some operational failure.

In present day electronic control devices, it is necessary that there be provided means for rendering the control device inoperative Whenever there are certain types of operational failures to prevent the control device from damaging controlled equipment. For example, in motor control circuits where electronic means are provided for energizing the same, it is essential that this electronic means not energize the motor or its circuits in such a manner as to cause damage thereto. If, as in the present arrangement, an alternating current powered amplifier and phase discriminator circuit is used to reversibly energize a controlled motor, the discriminator circuit must not operate to indicate a need for operation of the controlled motor in both directions at the same time as such indication would cause excess heating in the motor circuit. To prevent such heating, it is necessary that the discriminator circuit be so biased as to prevent operation of both sections thereof at the same time under normal operation and to render the discriminator circuit inoperative in the event there is a failure in the amplifier or power circuits feeding into the discriminator stage.

It is therefore an object of the present invention to provide for use with an electronic control having a phase discriminator circuit for preventing operation of the discriminator circuit when there is malfunctioning in the power supply cir cuits of the control.

A further object of the present invention is to provide for use With an electronic control having a phase discriminator circuit for rendering inoperative the discriminator circuit whenever 2. normal biasing voltage therein is removed.

Still another object of the present invention is to provide, in an electronic motor control circuit having thermionic discharge devices with cathode heaters, means for rendering said heaters ineffective when there is a power failure in the control circuit.

A still further object of the present invention is to provide, in an electronic motor control apparatus for a reversible motor, means to prevent e ization of said motor in both directions at the same time to eliminate heating in the motor circuits.

These and other objects of the invention will be understood upon considering the following specification and drawing which shows a circuit embodying the features of the invention.

In the drawing a single amplifier stage l0 provides a signal input to an alternating current phase discriminator stage i l which in turn controls a load device l2. A full wave rectifier circuit l3 provides the anode to cathode power supply for the amplifier stage. A transformer l4 having a primary i5 energized from alternating power line leads I6 and I1 furnishes the power for the rectifier circuit and the discriminator stage. Transformer l4 also has a secondary 2% center tapped at terminal 83, a secondary 2|, center tapped at terminal 52, and a further secondary 22.

Amplifier stage II] comprises a tube 23 having an anode 24, a control electrode 25, a cathode 26 and a cathode heater 21, the latter of which is energized from transformer secondary 22 through leads 3'! and 40. The cathode 26 is connected to a ground terminal 30 through lead 3|. The control electrode 25 is connected to a ground terminal 32 through a grid resistor 33. An alternating voltage control signal normally is impressed between the control electrode 25 and cathode 26 through input leads 3i and 35. Lead 35 is connected to a ground terminal 36.

The full wave rectifier stage l3 comprises a tube 4| having a pair of anodes 42 and as, a cathode 44 and a cathode heater 65. The heater .5 is connected to transformer secondary 22 through leads and 46, and leads 5! and 31.

- Anodes 42 and 43 of the rectifier tube are con- Located in the cathode circuit of rectifier tube 4| is a control relay 6| having a relay winding 60 which is operable when energized to move an associated switch blade |3| into engagement with an associated switch contact l30. Also associated with the rectifier portion of the apparatus is a biasing resistor 55. A complete electrical circuit may be traced from the end terminals of the secondary 2|, through conductors and 5| to anodes 42 and 43 respectively, cathode lead 5'1, relay winding so, grounds and 53, resistor 55 and lead 54 back to tap 52 on secondary 2|. When there is current flowing in the last traced circuit, there will be a voltage drop across the relay winding 6|] such that the right hand terminal will be positive with respect to grounded terminal. There will also be a voltage drop across the biasing resistor such that the upper terminal will b negative with re "23st to the lower or ground terminal.

The supply voltage for the amplifier stage it is taken from the voltage drop across the relay winding 60. This supply circuit may be traced from the right end of winding or the positive end, through lead 62, plate load resistor lead 64, anode 24, cathode 26, lead 3|, and grounds 3!! and 56 back to the relay winding A coupling capacitor 93 is located between the out put of amplifier stage it and the input of dis criminator stage II.

Discriminator stage It comprises a pair of tubes 65 and T2. Tube Elli has an anode on, a control electrode til, a cathode lit, and a cathode heater "II. Tube l2 has an anode it, a control electrode M, a cathode l5, and a cathode heater [6. Located in the output of the tube to is a control relay ill which has a relay winding and a switch blade [t5 normally biased out of engagement with an associated switch contact I04. Located in the output of tube l2 is a further control relay Bil having a relay winding and a switch blade Hil which is normally biased out of engagement with an associated contact I05. Capacitors Hi2 and IEid are connected in parallel with relay windings and ill, respectively, to bypass alternating current flowing in the output circuits of tubes and i2 and to maintain the relays continuously energized when. there is current flowing in the outputs. A pair of grid current limiting resistors, 95 and till are connected to control electrodes 8? and respectively. The discriminator tubes 65 l?! are so connected to the secondary 2!] that the tubes will be normally conductive on opposite half cycles of the alternating power source. The circuit for tube 55 may be traced from the upper terminal of secondary Ell through lead 82, winding 80, lead ll, anode 66, cathode ill, leads Elli and 84 back to the tap 83 on secondary 2c. The circuit for tube 12 may be traced from the lower terminal of secondary 20, through lead 9 I, winding 81, lead 85, anode 73, cathode [5, leads and 84 to the tap 83 on secondary 2n.

Controlled by the relays 8i and 93 is the load device I2 which comprises a reversible motor having a rotor lIll, a permanent magnet field II I and a pair of brushes l I2 and H3 making connection to the armature IIll. Supplying power to the motor is a battery II? which may be connected in parallel with a portion of a resistor IIB, center tapped at The l IL and H3 are connected through leads lM II5 to the ends of resistor i It so that the ture II i! will have a voltage applied thereto whenever either of relays Si or so are energized to close their respective contacts I BG-IL5, or 185-157, to connect the battery II! to the resistor H6. The polarity of the voltage on resistor Hi5 will be dependent upon which of the relays, 81 or Gil, is operative. The reversal. of polarity will cause reversal of operation of the rotor I In.

the

Operation In considering the operation of the present invention, it will be first assumed that apparatus is completely deenergized with no power being supplied to the input power leads it and 57. Under these circumstances, the apparatus will be deenergized and the components will be in the position shown upon the drawing. This will mean that all of the control relays will be deenergized and their associate switch contacts will be open.

soon as power is applied to the input power lines is and H, power will be supplied to the primary winding is of transformer 14. With the power being supplied to transformer M, the secondary 2.: will be supplying an energizing voltage for the cathode heater 45 of rectifier 4| and the cathode heater ill of amplifier tube 23. After these cathode heaters have been energized for a predetermined. time, their associated cathodes will become electron emissive and it will be possible for current to flow through the tube. 'Jhen current starts to flow through the rectifier tube ll, through the c' cuit as trace above, the current flow will cause a voltage drop across the relay winding 56 and a further volt-- age drop across the biasing resistor 55. When the current flow becomes great enough, the relay ti will become sufiiciently energized to move the switch blade it! into engagement with contact Hit. The closing of these contacts will result in the supplying of power to the cathode heaters H and of discriminator tubes and 12 respectively. This energizing circuit may be traced from the upper terminal of secondary 22 th 0" 3h leads ii! and 32, switch blade I3I, wi .11 contact 139, lead I33, heaters H and H5, connected in parallel, leads H5 and 37 back to the lower terminal of secondary 22.

When. the current flow in the rectifier circuit sufficient to energize the control relay 5!, the voltage drop across the biasing resistor 55 will be sulficient to apply an appreciably negative voltage to the control electrodes 51 and Id of minator tubes 55 and 12, respectively. This .ng voltage may be traced from the upper, or negative terminal of biasing resistor 55 through. lead Kill and resistor IllI to control electrode M from leads I2! and Hill and resistor till to control electrode 61. Inasmuch as the lower terminal of resistor 5'5 is connected to ground 53 and the cathodes ill and ll? of the disci nator tube are connected to ground at E l, there will be applied to the control electrodes of the discriminator tubes a voltage which is sufficiently negative on the control electrodes to maintain both of these tubes non-conductive in the absence of any further control signals on the input to the tubes.

When there is a voltage across the relay EH which is sufficient to energize the same, that voltage will also be sufficient to supply an energizing voltage for the amplifier tube so that when the cathode heater of tube 23 has heated the associated cathode to be electron emissive, there will be current flow in the amplifier stage which will make possible the amplifying of any input signals to the circuit.

In the absence of an input signal to the amplifier stage IQ, and with power supplied to the transformer Hi, the relay SI will be energized and the control relays SI and 9 3 will be decnergised since their associated discriminator tubes 65 and i2 will be biased to be nonconductive by the voltage drop across the biasing resister 55. As soon as an input signal is applied to the input leads S4 and 35, this signal will be amplified by the amplifier tube 23 and the signal will through the coupling capacitor 93 and be applied to the control electrodes 51 and M of the discriminator tubes 55 and I2.

The frequency of the input signal will correspond to the frequency of the power supply on input leads l5 and I! but the phase of the input signal on leads 34 and 35 may be reversed by any suitable control device, not shown. The phasing of the input signal will determine which of the discriminator tubes will be conductive. If the phasing on the output of the amplifier tube 23 is such that the control electrode til will be on the positive half cycle when the anode 66 is positive, the tube 65 will be conductive to energize the control relay Winding 35. If the control signal on the output of amplifier tube it is reversed in phase, the control electrode 14 will be positive on the opposite half cycle and will be positive at the same time that the anode i3 is positive so that the tube 12 will be conductive to energize the control relay winding. Bl. When either of relays 8| or 90 is energized, the corresponding contact in load circuit i2 will be energized and the battery Ill will be connected to resistor H6 to cause rotation of the rotor i it in one direction or the other depending upon which of the relays is energized. It should be noted that in the absence of any control signal, the negative bias on the control electrode 6'! and M is sufficient to maintain both of the tubes 65 and 12 non conductive so that the relays 5i and 99 will be deenergized. It is therefore necessary that the input control signal from the amplifier tube H] be sufficient to overcome this negative bias to render either of tubes 85 or 5'2 conductive.

In the event there should be a failure in the rectifier circuit, it is essential that the discriminator tubes 65 and 12 be rendered inoperative to prevent energization of relays 8i and 9!). Upon such a failure, there will be no direct current voltage supply to the amplifier stage It and therefore any input control signals will not be amplified. Also, upon a failure of the rectifier circuit, there will be no biasing voltage across the resistor 55. With no biasing voltage across the resistor 55 the control electrodes 61 and M will tend to assume the same potential as the cathodes and i5 and, lacking further protection, the discriminator tubes 65 and 12 will become conductive to energize relays 8! and 95] at the same time. By'providing the relay Bl in the rectifier circuit and arranging these circuits so that the relay is energized only when the rectifier is operating properly, it will be seen that a failure of the rectifier will cause the relay to be deenergized so that switch blade 13! will move out of engagement with switch contact Hi The opening of this switch contact will result in the deenergization of the heaters H and lo and the discriminator tubes will be rendered inoperative.

In the event that the relays a! and 9t wer both energized at the same time by the discriminator tubes 65 and i2, both sets of relay contacts ltd-JIM and Itt-iill in the load circuit would be closed so, that the battery ll'l would be connected across the upper and lower portions of resistor [5. Such a connection as this will cause excess heating in the resistor and is apt to cause damage thereto. There is also a tendency, with both of the relays energized, for the motor to drift as the electrical circuit may not be complete y balanced so that there will be circulating current flowing through the rotor ill) causing it to rotate. Thus, by opening the cathode heater circuit or" the discriminator tubes 55 and 12, it is possible to prevent energization of the control relays 8i and 9% whenever there has been a failure in the rectifier circuit l3.

It will be seen from the above that there has been provided a circuit for protecting against failures in the control apparatus which might cause damage to the control or load circuits. It will further be noted that the protective circuits have been utilized to supply operating voltages for the rest of the control apparatus when the rectifier circuit is operating normally.

It is to be understood that I have shown only one embodiment of my invention and various modifications thereof will be readily apparent to those skilled in the art. I have therefore intended the scope of the present invention to be limited solely by the appended claims;

I claim as my invention:

1. An electronic circuit comprising, in combination: a first stage including an electron tube; a second stage including a first electron tube and a second electron tube each having an anode, a cathode, a cathode heater and a control electrode; a rectifier stage; a rela connected in the output circuit of said rectifier, said relay comprising a relay winding and a pair of contacts; "an alternating voltage source; means connecting said source in energizing relation to said heaters, said rectifier stage and said tubes in said electrical connections between said rectifier stage and the tube in said first stage such that the output from said rectifier stage supplies an energizing voltage to the tube in said first stage; electrical connections between said rectifier stage and the control electrodes and cathodes in the tubes in said second stage such that operation of said rectifier stage results in a negative potential being impressed on said control electrodes with respect to said cathodes; and means including said relay for opening the energizing circuit to said heaters upon said rectifier stage being inoperative.

2. An electronic protective circuit comprising in combination; an amplifier circuitincluding an electronic discharge device having a cathode, an anode, and a control electrode, an alternating source of current, a current responsive means, and circuit means connecting directly in series said cathode, said anode, said source of current, and said responsive means; a rectification circuit connected to appi a control voltage to said discharge device, said circuit including a rectifier, a second source of alternatin current, and circuit means connecting in series said rectifier and said second source of current, said rectification circuit having a pair of terminals thereon; current responsive means connected to said terminals; and means including said responsive means connected in controlling relation to said first alternating source of current to effect energization of said amplifier only when said rectification circuit is operative.

3. In combination: a first circuit comprising an electron tube including an anode and cathode; a second circuit comprising first and second electron tubes each including an anode, a cathode and a cathode heater; a third circuit comprising a rectifier; means energizing said tubes in said second circuit, said rectifier, and said heaters in the tubes in said second circuit; electrical connections between said tube in said first circuit and the rectifier output circuit such that operation of said rectifier causes a positive potential to be impressed upon the anode of the tube in the first circuit with respect to thecathode; current re-v sponsive means; and .seans including said responsive means connected in controlling relation to said means energizing said heaters to effect energization of said heaters only when said rectifier is operative.

4. In combination: a first electron tube including an anode'and a cathode; a second and a third electron tube each including an anode, a cathode, a control electrode and a cathode heater; a rectifier; means energizing said second a I said third tubes, said heaters and said rectifier; electrical connections between said first tube and the rectifier output circuit such that said first tube has a positive anode potential with respect to its cathode uponenergization of said rectifier; a resistor connected in the rectifier output cir-- cult and the control electrode to cathode circuits of said second andsaid third tubes, said resistor having a voltage drop thereacross upon conduc tionof said rectifier, said voltage drop being of" feotive to place a negative'potential on e control electrodes of said second and said th with respect to the cathodes; and a relay having a winding in the output circuit of the rectifier, said relay being effective when energized to complete the energizing circuit to the heaters of sec-- 0nd and said third tubes.

5. An electronic protective circuit comprising in combination; a discriminator ci c including a pair of electronic discharge devices having an anode, a cathode, and a control ctrode, a source of alternating current, said source having two end terminals anda center tap thereon, a pair of current responsive devices, circuit, means connecting one of said. anodes through one of. current responsive devices to one oi rid t minals, circuit means connecting the other of said anodes through the other of said .ot responsive devices to the other of term circuit means connecting said cathodes to sa d center tap; a rectification circuit connected to apply a control voltage to said discharge devices, said circuit including a rectifier, a second "'elCE of alternating current, and circuit means interconnecting said rectifier and said second source of alternating current, said rectification circuit having a pair of terminals thereon; condition rcsponsive means connected to said terminals; and means including said condition. responsive connected in controlling relation to first source of alternating current to effect energisation of said discriminator circuit only when said rectification circuit is operative.

6. In combination: a first circuit comprising an electron tube including an anode and a cathode; a second circuit comprising an electron tube including an anode, a cathode and a cathode heater; a third circuit comprising a rectifier;

means energizing said tube in said second circuit,

said rectifier and said heater th tube in said second circuit; an electrical connection between the anode and cathode of the tube in said first circuit and the rectifier output circuit such that operation of said rectifier results in a positive potential being impressed upon the of the tube in said first circuit with respect to the oathode; current responsive means and means in-- eluding said responsive means connected in coni trolling relation to said means energizing said heater to effect energization of said heater only when said third circuit is operative.

'7. In combination: a first circuit comprising an electron tube including an anode-and a cathode; a second circuit comprising an electron tube including an anode, a cathode, a cathode heater and a control electrode; a third circuit comprising a rectifier tube; means energizing said tubes in said second and third circuits and said heater in the tube in the said second circuit; electrical connections between said tube in said first circult and the rectifier tube output circuit such iii) that said tube in said first circuit is energized upon operation of, said rectifier tube; electrical,

connections between the control electrode and cathode of the tube in said second circuit and the rectifier tube output circuit such that operation of, said rectifier, tube impresses a negative potential on the control electrode with respect to th cathode; current responsive means; and means including said responsive means connects, in controlling relation to said means energizing said heater to efiect energization of said heater only when said third circuit is operative,

8. In combination: an alternating current phase discriminator circuit comprising a first and a second tube eachhaving an anode, a cathode, a cathode heater, and a control electrode; a rectifier; a relay having a winding in the rectifier output circuit; a resistor in the rectifier output circuit; means energizing said discriminator circuit, said rectifier and, said cathode heaters; means connecting said relay in said heater energizing circuits such that energization of said relay winding upon energization of said rectifier operates to close the contacts of said relay to complete the energizing circuits to saidheaters; and said resistor being connected between the control elec trodes and cathodes of the tubes in said discriminator circuit such that a voltage drop across said resistor due to energization of said rectifier operates to place a negative'voltage on said control electrodes with respect to said cathodes.

9. In. combination: a first electron tube comprising an anode and a cathode; an alternating current phase discriminator circuit comprising a second and a third tube each having an anode, a

cathode, a cathode heater and a control electrode; an input circuit and an output circuit for said first tube; an input circuit and an output circuit for said discriminator circuit means connecting the output circuit for said first tube to the input circuit for saiddiscriminator circuit; a rectifier; a relay having a winding in the rectifier output circuit; a resistor in the rectifier output circuit; means energizing said discriminator circuit, said rectifier and said cathode heaters;

means connecting said relay in said heater energizing circuits such that energization of said relay winding upon energization of said rectifier operates to close the contacts of said relay to complete the energizing, circuits to said heaters; said resistor being connected between the control electrodes and cathodes of the tubes in said discriminator circuit suchv that a voltage drop across said resistor due to energization of said rectifier operates to place a negative voltage on said control electrodes with respect to said cathodes and means connecting the anode and cathode of said first tube across the relay winding in the rectifier outputcircuit such that a positive voltage is placed on the anode of said first tube with respect to the cathode upon energization of said rectifier.

HARRY M. WILSON.

REFERENCES CITED ihe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,866,459 Gebhard so July 5, 1932 2,402,472 Usselman June 18, 1946 2,457,112 Abercrombie et al. Dec. 28, 1948 

